This invention relates to a method of making a composite abrasive compact.
Abrasive compacts are used extensively in cutting, milling, grinding, drilling, boring and other abrasive operations. Abrasive compacts consist of a mass of diamond or cubic boron nitride particles bonded into a coherent, polycrystalline conglomerate. The abrasive particle content of abrasive compacts is high and there is generally an extensive amount of direct particle-to-particle bonding. Abrasive compacts are made under elevated temperature and pressure conditions at which the abrasive particle, be it diamond or cubic boron nitride, is crystallographically stable.
Diamond abrasive compacts are also known as polycrystalline diamond or PCD and cubic boron nitride abrasive compacts are also known as polycrystalline CBN or PCBN.
Abrasive compacts tend to be brittle and in use they are frequently supported by being bonded to a cemented carbide substrate or support. Such supported abrasive compacts are known in the art as composite abrasive compacts. Composite abrasive compacts may be used as such in a working surface of an abrasive tool.
In making abrasive compacts, particles of a single size or a mixture of particles of various sizes may be used. Examples of such compacts are disclosed in U.S. Pat. Nos. 4,604,106 and 5,011,514.
It is also known to produce an abrasive compact which has two zones differing in particle size. Examples of such compacts are described in U.S. Pat. Nos. 4,861,350 and 4,311,490.
European Patent No. 0 626 236 describes a method of making an abrasive compact which includes the step of subjecting a mass of ultra-hard abrasive particles to conditions of elevated temperature and pressure suitable for producing an abrasive compact, the mass being characterised by at least 25% by mass of ultra-hard abrasive particles having an average particles size in the range 10 to 100 microns and consisting of particles having at least three different particle sizes and at least 4% by mass of ultra-hard abrasive particles having an average particles size of less then 10 microns. The particle mix thus contains four different sizes of particles. The specification discloses the advantages of using such a mixture of particles in producing abrasive compacts in turning and shaper tests.
European Patent No. 0 626 237 discloses a method of making an abrasive compact which includes the step of subjecting a mass of ultra-hard abrasive particles to conditions of elevated temperature and pressure suitable for producing an abrasive compact, the mass being characterised by the ultra-hard abrasive particles having an average particle size of less than 20 microns and consisting of particles having three different average particle sizes.
Composite abrasive compacts of the type described above are used in a variety of applications. One such application is as an insert for drill bits. Such bits including percussion bits, rolling cone bits and drag bits. For drill bits, the diamond compact layer is generally fairly thick, e.g. having a thickness of up to 5 mm. In the manufacture of composite diamond compacts, stresses arise in the diamond compact layer. These stresses are caused, in part, by a difference in the thermal coefficient of expansion between the diamond layer and the substrate. Such stresses give rise to several problems. For example delamination of the diamond layer from the substrate can occur when the composite diamond compact is brazed to a working surface of a tool. Further, the stresses in the diamond layer can lead to spalling or chipping of the diamond layer, in use.